Batteries typically are constructed with a set of anode plates and a set of interleafing cathode plates, which are spaced apart by separators infused with an electrolyte. The anode plates must be electrically connected to the battery anode terminal, and the cathode plates must be electrically connected to the battery cathode terminal. For the sake of rigidity of the assembled sets of anode and cathode plates, the connection between the plates and the terminals is typically mechanical as well as electrical, and is accomplished with an "end connector" of some type.
This electromechanical attachment of the anode and cathode plates to their respective terminals through end connectors is one of the more labor intensive and fault intensive aspects of battery construction. Ideally, the end connector assembly would rigidly support the plates to help prevent their deformation within the battery case and to resist vibrational damage to the plates and separators. Further, the end connectors should be formed of a material that is readily connectable to both the terminal and to the plates in a manner that assures an easy and dependable electrical and mechanical attachment. It is particularly important that the electrical connection to both the plates and the terminal be of the lowest possible resistance, or at least of a resistance no greater than the resistance in the plates and terminals themselves, so that the impedance of the connection is minimized and the current capacity is maximized.
These goals become extremely important in a battery with extremely thin plates, as described in U.S. Pat. No. 5,047,300, of which this application is a continuation-in-part, and U.S. Pat. No. 5,045,086. Briefly, those applications disclose a rechargeable battery with a mechanical design characterized by very thin anode and cathode plates that may be spirally wound with a electrolyte pasted separator. The resulting wound battery generally has little structural strength and therefore requires extra support from the battery casing. Further, the very thin plates and separators result in a very large number of plates at each end. The large number of plates requires a proportionately large number of labor intensive and failure prone connectors, in comparison to batteries having thicker plates and separators.
The dominant electrical characteristic of the batteries described in the above-mentioned applications is a very high charge and discharge rate. This high charge and discharge rate requires high current carrying capacity in the electrical connection from the plates to the terminals, in order to both carry the load without reducing the charge and discharge rate and also to avoid resistive overheating that could structurally or electrically damage the battery.
The prior art discloses many types of end connectors that are designed to enhance the structural integrity or to minimize the electrical impedance of batteries. For example, U.S. Pat. No. 4,539,273 by Goebel describes a set of plates wound on a spool with an anode flange and a cathode flange. Each plate has a set of connecting tabs spaced along an edge, which is in electrical contact with the appropriate spool flange. The Goebel device does not provide for any secure mechanical connection between the spool flange and the plates. Also, the Goebel device would appear to require a fairly intricate manufacturing process, especially if used on a very thin plate battery having a very long plate edge that would require a large number of connecting tabs.
In U.S. Pat. No. 3,695,935 by Cromer, there is disclosed a spirally wound plate design where the anode plate is wound offset from the cathode plate so that the anode plate edge overhangs one edge of the spiral and the cathode plate edge overhangs the other edge of the spiral. The two overhanging edges are "ruffled". The purpose of the ruffles is said to be to strengthen the edges against damage during manufacturing, to blunt the edges to reduce the potential for injuring manufacturing workmen, and to increase the ohmic contact between the plate and the terminal. The Cromer device still uses an ordinary strap type end connector to join the plates to the terminal.
One of the more common arrangements for electrically connecting the plates to the terminals is shown in U.S. Pat. No. 3,862,861 by McClelland et al. In the McClelland arrangement, the plates include spaced tabs on the plate edge so that the wound plate has a set of tabs protruding from an end. The protruding tabs are then joined together and connected to the terminal. The McClelland arrangement has the problems of difficulty in construction and increased impedance that are typical of the prior art.